Semiconductor device

ABSTRACT

A semiconductor device mountable on a wiring board with the bottom surface being opposed to the wiring board. The semiconductor device includes: a semiconductor chip; a mold resin encapsulating the semiconductor chip; a first heat spreader joined to the semiconductor chip on the bottom surface side, and extending in almost parallel with the bottom surface with both ends thereof protruding from an edge of the mold resin, the first heat spreader being capable of being joined to the wiring board at the both ends thereof; and a second heat spreader joined to the semiconductor chip on a top surface side, and extending in almost parallel with the bottom surface to cross with the first heat spreader with both ends thereof protruding from the edge of the mold resin, the second heat spreader being capable of being joined to the wiring board at the both ends thereof. One of the first and second heat spreaders is a lead frame electrically connected to the semiconductor chip.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a semiconductor devicecomprising a semiconductor chip encapsulated with a mold resin, and moreparticularly to a semiconductor device comprising a semiconductor chipgenerating a large quantity of heat, encapsulated with a mold resin.

[0003] 2. Description of Related Art

[0004] Because a semiconductor chip is encapsulated with a mold resin(an encapsulating resin) in a semiconductor device, heat generated inthe semiconductor chip readily resides within the semiconductor device(a mold resin). It is therefore necessary for a semiconductor deviceprovided with a semiconductor chip that generates a large quantity ofheat while it is driven to efficiently dissipate heat generated in thesemiconductor chip to the outside of the semiconductor device.

[0005] For example, Japanese Unexamined Patent Publication No.60-160639(1985) has disclosed a semiconductor device, in which a leadframe joined to one surface of the semiconductor chip is exposed througha mold resin in the vicinity of the joint to the semiconductor chip.With this semiconductor device, heat generated in the semiconductor chipis chiefly dissipated to the outside via the exposed portion of the leadframe through the mold resin.

[0006] Also, Japanese Unexamined Patent Publication No. 8-298302(1996)and Japanese Unexamined Patent Publication No. 10-321768(1998) havedisclosed a semiconductor device, in which a heat-spreading plate or aheat-spreading body joined to one surface of the semiconductor chipinstead of the lead frame is exposed to the outside of a mold resin.With this semiconductor device, heat generated in the semiconductor chipis chiefly dissipated to the outside via the exposed portion of theheat-spreading plate or heat-spreading body through the mold resin.

[0007] Further, there is known a semiconductor device, in which thesemiconductor chip is directly exposed through the mold resin. Thissemiconductor device is shaped like a rectangular prism, and thesemiconductor chip is exposed through the center of one surface of thesemiconductor device. Heat generated in the semiconductor chip is thusdirectly dissipated to the outside of the semiconductor device. Thissemiconductor device is mounted on a wiring board in an orientation suchthat the surface from which the semiconductor chip is exposed opposesthe wiring board.

[0008] In the case of the semiconductor chip generating a large quantityof heat, however, the semiconductor device having the structuredescribed above is not able to dissipate heat generated in thesemiconductor chip in a satisfactory manner, and there has been a needfor a semiconductor device with an enhanced heat-spreading capability.

[0009] In addition, a semiconductor device in which the semiconductorchip is exposed directly through the mold resin has a problem that thesemiconductor chip readily breaks. Further, in a case where the exposedsemiconductor chip is joined to the wiring board through soldering orthe like in such a semiconductor device, because the joint is hidden ina space between the semiconductor device and the wiring board, directvisual inspection of the joint is impossible, which makes it difficultto confirm whether the two components are joined to each other in asatisfactory manner.

SUMMARY OF THE INVENTION

[0010] An object of the invention is therefore to provide asemiconductor device capable of enhancing the heat-spreading capability.

[0011] Another object of the invention is to provide a semiconductordevice enabling a joint state to the wiring board to be readilyconfirmed when joined to the wiring board.

[0012] A semiconductor device of the invention is a semiconductor devicehaving a bottom surface and mountable on a wiring board with the bottomsurface being opposed to the wiring board. The semiconductor deviceincludes: a semiconductor chip; a mold resin encapsulating thesemiconductor chip; a first heat spreader joined to the semiconductorchip on the bottom surface side with respect to the semiconductor chip,and extending in substantially parallel with the bottom surface withboth ends thereof protruding from an edge of the mold resin when viewedin a direction perpendicular to the bottom surface, the first heatspreader being capable of being joined to the wiring board by means ofthe both ends thereof; and a second heat spreader joined to thesemiconductor chip on a top surface side opposite to the bottom surfacewith respect to the semiconductor chip, and extending in substantiallyparallel with the bottom surface to cross with the first heat spreaderwith both ends thereof protruding from the edge of the mold resin whenviewed in a direction perpendicular to the bottom surface, the secondheat spreader being capable of being joined to the wiring board by meansof the both ends. The semiconductor device is arranged in such a mannerthat one of the first and second heat spreaders is a lead frameelectrically connected to the semiconductor chip, and that heatgenerated in the semiconductor chip is dissipated via the first heatspreader and the second heat spreader.

[0013] According to the invention, the semiconductor chip is providedbetween the first and second heat spreaders, and heat generated in thesemiconductor chip is thereby dissipated via the first and second heatspreaders. In a case where the lead frame, a heat-spreading plate, or aheat-spreading body is joined to only one surface of the semiconductorchip as in the conventional semiconductor device, heat generated in thesemiconductor chip is dissipated from substantially one side withrespect to the semiconductor chip.

[0014] In contrast, according to the semiconductor device of theinvention, heat generated in the semiconductor chip is dissipated in twodirections (from the bottom surface side and the top surface side of thesemiconductor device) with respect to the semiconductor chip, alongwhich the first and second heat spreaders are provided, respectively.Further, because the first and second heat spreaders cross with eachother, heat transmitted to the first and second heat spreaders isdissipated as it is transmitted in two directions along each lengthdirection of the first and second heat spreaders, that is, in fourdirections with respect to the semiconductor chip when viewed in adirection perpendicular to the bottom surface. This semiconductor devicetherefore has the higher heat-spreading capability than the conventionalsemiconductor device.

[0015] It is preferable that the first and second heat spreaders have alarge area, and for example, it may be arranged in such a manner thatthe semiconductor chip falls within an intersection between the firstand second heat spreaders completely when viewed in a directionperpendicular to the bottom surface. In this case, the heat-spreadingcapability can be enhanced further.

[0016] Also, because the semiconductor device can be joined to thewiring board by means of the both ends of the first and second heatspreaders, the joint strength with respect to the wiring board can beincreased. Further, the first heat spreader may be exposed to the bottomsurface of the semiconductor device. In this case, the semiconductordevice can be joined to the wiring board at the portion of the firstheat spreader exposed to the bottom surface in addition to the both endsof the first and second heat spreaders. Because a larger joint surfaceto the wiring board can be secured in this case, the joint strengthbetween the semiconductor device and the wiring board can be increasedfurther.

[0017] Further, because the both ends of the first and second heatspreaders protrude from the edge of the mold resin when viewed in adirection perpendicular to the bottom surface, direct visual inspectionof the joints of the semiconductor device (the both ends of the firstand second heat spreaders) to the wiring board becomes possible. Thejoint state of the semiconductor device to the wiring board can be thusreadily confirmed.

[0018] The semiconductor chip may be electrically connected to thewiring board via one of the first and second heat spreaders that is ineffect a lead frame.

[0019] Both of the first and second heat spreaders may be lead frameselectrically connected to the semiconductor chip.

[0020] According to this arrangement, the semiconductor chip can beelectrically connected to the wiring board via the first and second heatspreaders.

[0021] The semiconductor chip may be provided with a field effecttransistor having a source electrode and a drain electrode. In thiscase, the drain electrode may be electrically connected to the firstheat spreader, and the source electrode may be electrically connected tothe second heat spreader.

[0022] In the case of a semiconductor chip provided with a field effecttransistor (FET), the semiconductor chip generates heat when a currentflows between the source electrode and the drain electrode. According tothe arrangement of the invention, heat generated in the FET can bedissipated to the outside of the semiconductor device in a satisfactorymanner. The FET maybe, for example, a MOS FET (Metal-Oxide-SemiconductorField Effect Transistor) The semiconductor chip may be connectedwirelessly to one of the first and second heat spreaders. “To beconnected wirelessly” referred to herein is defined as a state where thesemiconductor chip is provided in close proximity to the lead frame andjoined thereto not through a bonding wire, such as a gold line, butthrough the use of a joining material (for example, soldering).

[0023] According to this arrangement, the semiconductor chip and thefirst or second heat spreader are provided in close proximity andelectrically connected to each other not through a bonding wire butthrough the use of a joining material, such as soldering; moreover, theyare mechanically connected to each other as well. Heat generated in thesemiconductor chip is thus transmitted efficiently to the first orsecond heat spreader via the wirelessly connected portion. Thissemiconductor device therefore has a high heat-spreading capability.

[0024] In this case, by using sufficiently large first and second heatspreaders, not only can the heat-spreading capability be enhanced, butalso the joint strength between the semiconductor chip and the first orsecond heat spreader can be increased.

[0025] In a case where both of the first and second heat spreaders arelead frames electrically connected to the semiconductor chip, it ispreferable that the semiconductor chip is connected wirelessly to bothof the first and second heat spreaders. In this case, heat generated inthe semiconductor chip is transmitted to both of the first and secondheat spreaders in a satisfactory manner, and the semiconductor devicearranged in this manner therefore has a high heat-spreading capability.

[0026] The second heat spreader may be joined to the wiring board whilebeing electrically isolated therefrom. In other words, the second heatspreader may not contribute to electrical connection between thesemiconductor chip and the wiring board. In this case, the semiconductorchip is electrically connected to the wiring board via the first heatspreader, while heat generated in the semiconductor chip is dissipatedto the outside of the semiconductor device via the first and second heatspreaders.

[0027] The second heat spreader may have a heat-spreading portionexposed through the mold resin on the top surface side of thesemiconductor device.

[0028] According to this arrangement, heat generated in thesemiconductor chip can be dissipated to the outside of the semiconductordevice through a short distance via the heat-spreading portion.

[0029] The semiconductor device may further include a third heatspreader joined to the second heat spreader and exposed through the moldresin.

[0030] According to this arrangement, heat generated in thesemiconductor chip can be dissipated efficiently to the outside of thesemiconductor device via the third heat spreader exposed through themold resin. It is preferable that the exposed area of the third heatspreader is large. The third heat spreader may be provided with, forexample, a plurality of plate-shaped portions (fins)

[0031] The above and other objects, features, and advantages of theinvention will become more apparent from the following description ofembodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]FIG. 1 is a schematic perspective view showing the structure of asemiconductor device according to a first embodiment of the invention;

[0033]FIG. 2 is a schematic cross section of the semiconductor deviceshown in FIG. 1;

[0034]FIG. 3 is a schematic plan view of the semiconductor device shownin FIG. 1 when the top surface is viewed in a direction perpendicular tothe bottom surface;

[0035]FIG. 4 is a schematic perspective view showing the structure of asemiconductor chip;

[0036]FIG. 5 is a schematic bottom view of the semiconductor deviceshown in FIG. 1;

[0037]FIG. 6 is a schematic plan view of a wiring board on which thesemiconductor device shown in FIG. 1 is mounted;

[0038]FIG. 7(a) and FIG. 7(b) are schematic cross section and plan view,respectively, showing the structure of a semiconductor device accordingto a second embodiment of the invention;

[0039]FIG. 8(a), FIG. 8(b), and FIG. 8(c) are schematic plan viewsshowing the structures of semiconductor devices according to thirdthrough fifth embodiments of the invention, respectively; and

[0040]FIG. 9(a) and FIG. 9(b) are schematic perspective view and crosssection, respectively, showing the structure of a semiconductor deviceaccording to a sixth embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0041]FIG. 1 is a schematic perspective view showing the structure of asemiconductor device according to a first embodiment of the invention.

[0042] The semiconductor device 1 encloses a semiconductor chip providedwith a MOS field effect transistor (MOS FET), and is shaped like a flat,rectangular prism by a mold resin 5 encapsulating the semiconductorchip. Plural lead frames 3 (four of them in this embodiment) made ofmetal protrude from the mold resin 5 on respective side surfaces 2 ofthe semiconductor device 1 (surfaces parallel to the thickness directionof the semiconductor device 1). Also, a heat-spreading portion 6 made ofmetal is exposed through the mold resin 5 at the center of the surface4T, which is one of a pair of surfaces perpendicular to the thicknessdirection of the semiconductor device 1 (hereinafter, referred to as thetop surface). The exposed portion of the heat-spreading portion 6through the mold resin 5 is made into a flat plane, which is almostflush with the surface of the mold resin 5.

[0043] Of the two pairs of side surfaces 2 of the semiconductor device 1with each pair comprising the side surfaces 2 parallel to each other,the protrusions of the lead frames 3 from one pair of side surfaces 2Aform drain terminals 3D. Also, the protrusions of the lead frames 3 fromthe other pair of side surfaces 2B of the semiconductor device 1 formsource terminals 3S and gate terminals 3G. The gate terminals 3G areadjacent to one of the pair of side surfaces 2A.

[0044] The drain terminals 3D, the source terminals 3S, and the gatethermals 3G are all provided to the surface 4B side of the semiconductordevice 1 on the side opposite to the top surface 4T (hereinafter,referred to as the bottom surface). The surfaces of the drain terminals3D, the source terminals 3S, and the gate terminals 3G on the bottomsurface 4B side are almost flush with the bottom surface 4B of thesemiconductor device 1.

[0045]FIG. 2 is a schematic cross section of the semiconductor device 1taken along the section line II-II shown in FIG. 1. FIG. 3 is aschematic plan view of the semiconductor device 1 when the top surface4T is viewed in a direction perpendicular to the bottom surface 4B. Themold resin 5 is omitted from FIG. 3, and the edge of the mold resin 5 isindicted by a chain double-dashed line.

[0046] The lead frames 3 include plate-shaped first through third leadframes 8, 9, and 10 extending in substantially parallel with the bottomsurface 4B. The first lead frame 8, the second lead frame 9, and thethird lead frame 10 extend in directions such that the first lead frame8 and the last two lead frames 9, 10 are orthogonal to each other andthereby cross with one another. The first lead frame 8 is wider than thesecond and third lead frames 9 and 10, and the second lead frame 9 iswider than the third lead frame 10.

[0047] The both ends 8 a, 9 a, and 10 a of the first through third leadframes 8, 9, and 10, respectively, protrude from the edge of the moldresin 5 when viewed in a direction perpendicular to the bottom surface4B (see FIG. 3).

[0048] The first lead frame 8 is of a tabular shape such that can beplaced on substantially a single plane, and extends in a directionperpendicular to the sheet surface of FIG. 2. The first lead frame 8 isexposed from the bottom surface 4B. The both ends 8 a of the first leadframe 8 in its length direction are made into the shape of a comb, andthe ends of these comb-shaped portions protrude from the edge of themold resin 5 and form the drain terminals 3D (see FIG. 1). The base endsof the comb-shaped portions reside within the mold resin 5. Thisstructure makes the first lead frame 8 difficult to fall off from themold resin 5.

[0049] The second and the third lead frames 9 and 10 respectivelyinclude: both ends 9 a and 10 a placed on substantially the same planeas the first lead frame 8; intermediate portions 9 c and 10 c providedalong a plane spaced apart from the above-specified plane by a certaindistance; and rising portions 9 b and 10 b between the both ends 9 a and10 a and the intermediate portions 9 c and 10 c, respectively. Theintermediate portions 9 c and 10 c avoid the interference between thefirst lead frame 8 and the second and third lead frames 9 and 10.

[0050] The both ends 9 a of the second lead frame 9 are made into theshape of a comb, and the ends of these comb-shaped portions protrudefrom the edge of the mold resin 5 and form the source terminals 3S (seeFIG. 1). The base ends of these comb-shaped portions reside within themold resin 5. This structure makes the second and third lead frames 9and 10 difficult to fall off from the mold resin 5.

[0051] The both ends 11 a of the third lead frame 10 protrude from theedge of the mold resin 5 and form the gate terminals 3G.

[0052] The intermediate portion 9 c of the second lead frame 9 in thevicinity of the semiconductor chip 7 is made thicker so as to protrudein the direction opposite to the semiconductor chip 7, and forms theheat-spreading portion 6 exposed through the mold resin 5 on the topsurface 4T of the semiconductor device 1. In other words, theheat-spreading portion 6 forms part of the second lead frame 9.

[0053] The semiconductor chip 7 is provided in a space between the firstlead frame 8 and the intermediate portions 9 c and 10 c of the secondand third lead frames 9 and 10 in reference to the thickness directionof the semiconductor device 1. The semiconductor chip 7 is shaped like aplate, and the thickness direction of the semiconductor chip 7 and thethickness direction of the semiconductor device 1 agree with each other.The semiconductor chip 7 is provided in close proximity to the firstthrough third lead frames 8, 9, and 10, and joined thereto not through abonding wire but through soldering 15. In short, the semiconductor chip7 is connected wirelessly to the first through third lead frames 8, 9,and 10.

[0054] The rising portions 9 b are provided in such a way as to pass bythe vicinity of the side surfaces of the semiconductor chip 7 within themold resin 5.

[0055] When viewed in a direction perpendicular to the bottom surface4B, the semiconductor chip 7 is slightly smaller than a region 16(hereinafter, referred to as the overlap region) where the locations ofthe first lead frame 8, and second and third lead frames 9 and 10overlap (cross with each other), but has almost the same area as theoverlap region 16 (see FIG. 3). The entire semiconductor chip 7 isprovided within the overlap region 16, and the semiconductor chip 7overlaps the first through third lead frames 8, 9, and 10 in a largearea.

[0056]FIG. 4 is a schematic perspective view showing the structure ofthe semiconductor chip 7.

[0057] A source electrode 11S and a gate electrode 1G are formed on onesurface of the semiconductor chip 7. The area of the gate electrode 11Gis smaller than the area of the source electrode 11S. The gate electrode11G is provided in the vicinity of one side of the semiconductor chip 7when viewed in a plane looking down the semiconductor chip 7 in thethickness direction thereof. On the other hand, the source electrode 11Sis formed in a region avoiding the vicinity of the above-specified sideof the semiconductor chip 7.

[0058] A drain electrode 11D is formed on the other surface of thesemiconductor chip 7.

[0059] Referring to FIG. 3, when viewed in a direction perpendicular tothe bottom surface 4B, the entire source electrode 11S is positionedwithin the region where the second lead frame 9 is present, whereas thesource electrode 11S does not overlap the third lead frame 10. Thesemiconductor chip 7 is connected wirelessly to the second lead frame 9via the source electrode 11S, and the source electrode 11S and thesecond lead frame 9 are not only electrically connected, but alsomechanically joined to each other.

[0060] Likewise, when viewed in a direction perpendicular to the bottomsurface 4B, the entire gate electrode 11G is positioned within theregion where the third lead frame 10 is present, whereas the gateelectrode 11G does not overlap the second lead frame 9. Thesemiconductor chip 7 is connected wirelessly to the third lead frame 10via the gate electrode 11G, and the gate electrode 11G and the thirdlead frame 10 are not only electrically connected, but also mechanicallyjoined to each other.

[0061]FIG. 5 is a schematic bottom view of the semiconductor device 1,and shows a state when the bottom surface 4B is viewed in a directionperpendicular to the bottom surface 4B. The mold resin 5 is omitted fromFIG. 5, and the edge of the mold resin 5 is indicated by a chaindouble-dashed line.

[0062] The drain electrode 11D is formed at the center of thesemiconductor chip 7, and the drain electrode 11D has a large area,which is almost as large as (slightly smaller than) the area occupied bythe semiconductor chip 7. The semiconductor chip 7 is connectedwirelessly to the first lead frame 8 via the drain electrode 11D, andthe drain electrode 11D and the first lead frame 8 are not onlyelectrically connected, but also mechanically joined to each other.Because the drain electrode 11D has a large area, a larger joint area issecured for the semiconductor chip 7 and the first lead frame 8.

[0063] As has been described, the semiconductor chip 7 is sandwiched bythe first through third lead frames 8, 9, and 10 from the both sides (intwo directions) in reference to the thickness direction of thesemiconductor chip 7, and the joint area to the first through third leadframes 8, 9, and 10 becomes larger. This increases the joint strengthbetween the semiconductor chip 7 and the lead frames 3.

[0064]FIG. 6 is a schematic plan view of a wiring board on which thesemiconductor device 1 is mounted.

[0065] In the wiring board 12 are formed electrode pads 13D, 13S, and13G at positions corresponding to the drain terminals 3D, the sourceterminals 3S, and the gate terminals 3G, respectively. Wirings 14D, 14Sand 14G extend from the electrode pads 13D, 13S, and 13G, respectively.

[0066] Referring to FIG. 5 and FIG. 6, the semiconductor device 1 can bemounted on the wiring board 12 with the bottom surface 4B being opposedto the wiring board 12. In this instance, the drain terminals 3D, thesource terminals 3S, and the gate terminals 3G of the semiconductordevice 1 can be joined to the electrode pads 13D, 13S, and 13G of thewiring board 12, respectively, through soldering or the like.

[0067] The semiconductor device 1 can be joined to the wiring board 12in a large joint area by means of the drain terminals 3D, the sourceterminals 3S, and the gate terminals 3G protruding from the four sidesurfaces 2. It is thus possible to join the semiconductor device 1 tothe wiring board 12 with a high joint strength.

[0068] The wiring board 12 may be provided with a joining pad at aposition corresponding to the bottom surface 4B of the semiconductordevice 1. By joining the joining pad to the first lead frame 8 exposedto the bottom surface 4B through soldering or the like, the joint areaof the semiconductor device 1 and the wiring board 12 can be furtherincreased, which in turn increases the joint strength further.

[0069] Because the drain terminals 3D, the source terminals 3S, and thegate terminals 3G protrude from the side surfaces 2 of the semiconductordevice 1, direct visual inspection of the joints of the drain terminals3D, the source terminals 3S, and the gate terminals 3G to the wiringboard 12 (electrode pads 13D, 13S, and 13G) becomes possible. Hence,when the semiconductor device 1 is joined to the wiring board 12, thejoint state to the wiring board 12 can be readily confirmed.

[0070] Even in a case where the both ends of the lead frame 8 do notprotrude from the side surfaces 2A, that is, in a case where the bothends of the first lead frame 8 do not protrude from the edge of the moldresin 5 when viewed in a direction perpendicular to the bottom surface4B, the exposed portion of the first lead frame 8 from the bottomsurface 4B can be connected to the wiring board 12 as the drainterminal. In this case, an electrode pad can be provided to the wiringboard 12 in a region corresponding to the drain terminal.

[0071] In this case, however, the joint of the drain terminal (firstlead frame 8) and the corresponding electrode pad on the wiring board 12is hidden in a space between the semiconductor device 1 and the wiringboard 12, which makes the direct visual inspection of the joint as inthis embodiment impossible. Therefore, in this case, it is not easy toconfirm whether the drain terminal (first lead frame 8) is joined to theelectrode pad on the wiring board 12 in a satisfactory manner.

[0072] The semiconductor chip 7 generates heat when a current flowsbetween the source electrode 11S and the drain electrode 11D. In thisinstance, the semiconductor chip 7 generates a large quantity of heat.Heat generated in the semiconductor chip 7 is, however, transmittedefficiently to the first through third lead frames 8, 9, and 10 for thereasons as follows: (1) the semiconductor chip 7 overlaps the firstthrough third lead frames 8, 9, and 10 in a large area; and (2) thesource electrode 11S, the drain electrode 11D, and the gate electrode11G are connected wirelessly to the first through third lead frames 8,9, and 10.

[0073] Heat transmitted to the first through third lead frames 8, 9, and10 is dissipated into air via the drain terminals 3D, the sourceterminals 3S, and the gate terminals 3G, as well as the wirings 14D,14S, and 14G extending from the electrode pads 13D, 13S, and 13G towhich the drain terminals 3D, the source terminals 3S, and the gateterminals 3G are joined, respectively.

[0074] In this manner, heat generated in the semiconductor chip 7 isdissipated as it is transmitted not in a single direction, but in twodirections (a direction along which the first lead frame 8 is providedand a direction along which the second and third lead frames 9 and 10are provided) with respect to the semiconductor chip 7.

[0075] Further, heat transmitted to the first lead frame 8 and thesecond and third lead frames 9 and 10 is dissipated in two directionsalong the length direction of the first lead frame 8 and in twodirections along the length direction of the second and third leadframes 9 and 10, that is, in four directions with respect to thesemiconductor chip 7. This enhances the heat-spreading capability of thesemiconductor device 1.

[0076] Furthermore, heat transmitted to the second lead frame 9 isdissipated into air from the heat-spreading portion 6. Because theheat-spreading portion 6 is formed by making part of the second leadframe 9 thicker, heat generated in the semiconductor chip 7 isdissipated into air through a short distance. This effect also enhancesthe heat-spreading capability of the semiconductor device 1.

[0077] The semiconductor device 1 mounted to the wiring board 12 may beused with a fan being attached to a position at which air can be sent tothe semiconductor device 1. By sending air to the semiconductor device 1(particularly, to the heat-spreading portion 6) by means of the fan,heat generated in the semiconductor chip 7 can be dissipated into airmore efficiently.

[0078]FIG. 7(a) is a schematic cross section showing the structure of asemiconductor device according to a second embodiment of the invention,and FIG. 7(b) is a schematic plan view thereof. Components correspondingto those shown in FIG. 1 through FIG. 3 are labeled with the samereference characters in FIG. 7(a) and FIG. 7(b), and the description ofthese components is omitted.

[0079] The second lead frame 9 of the semiconductor device 21 has noheat-spreading portion 6, and has a constant thickness. The mold resin 5is provided with an opening 5 a at the center of the top surface 4T ofthe semiconductor device 21. Inside the opening 5 a appears a portion ofthe second lead frame 9 in the vicinity of the semiconductor chip 7.

[0080] A heat spreader 22 is fit into the opening 5 a. The heat spreader22 is joined to the second lead frame 9 through soldering, silver paste,etc.

[0081] The heat spreader 22 may pinch or may be pinched with the secondlead frame 9 or the mold resin 5. In other words, the heat spreader 22may come into direct contact with the second lead frame 9 withoutsoldering, silver paste, etc.

[0082] In this case, for example, the second lead frame 9 and the heatspreader 22 may be pinched together. To be more specific, part of thesecond lead frame 9 may be bent to come around above the heat spreader22 (in a direction opposite to the second lead frame 9) so as tosandwich the heat spreader 22. Alternatively, the end of the heatspreader 22 may come around and extend beneath the second lead frame 9(in a direction opposite to the heat spreader 22) so as to sandwich thesecond lead frame 9. In any of these cases, the mold resin 5 is formedafter the second lead frame 9 and the heat-spreading portion 22 arepinched together.

[0083] The heat spreader 22 is made of metal, and is provided with anumber of plate-shaped fins 22 p, which are substantially parallel tothe thickness direction of the semiconductor device 21 while beingparallel to one another. The fins 22 p are exposed to the outside of themold resin 5. This increases the exposed area of the heat spreader 22 incomparison with the exposed area of the heat-spreading portion 6 of thesemiconductor device 1 shown in FIG. 1, and thereby allowing the heatspreader 22 to come into contact with air in a larger area.

[0084] In the semiconductor device 21 having the structure describedabove, heat generated in the semiconductor chip 7 is dissipatedefficiently not only via the first through third lead frames 8, 9, and10, but also via the heat spreader 22. Because the exposed area of theheat spreader 22 is large, the semiconductor device 21 has the higherheat-spreading capability than the semiconductor device 1 shown in FIG.1.

[0085] The heat spreader 22 is not limited to the one having the fins 22p as shown in FIG. 7(a) and FIG. 7(b), and can be used in various formsas follows.

[0086]FIG. 8(a) through FIG. 8(c) are schematic plan views showing thestructures of the semiconductor devices according to third through fifthembodiments of the invention, respectively. Components corresponding tothe components of the semiconductor device 21 shown in FIG. 7(a) andFIG. 7(b) are labeled with the same reference characters in FIG. 8(a)through FIG. 8(c), and the description of these components is omitted.

[0087] The semiconductor device 25 of the third embodiment shown in FIG.8(a) is of a structure similar to that of the semiconductor device 21shown in FIG. 7(a) and FIG. 7(b); however, they are different instructure of the heat spreader. The heat spreader 26 provided to thesemiconductor device 25 is made of metal, and includes a number ofcoaxially aligned, cylindrical portions 26 p having different diameters.The cylindrical portions 26 p are exposed through the mold resin 5.

[0088] The semiconductor device 29 of the fourth embodiment shown inFIG. 8(b) is of a structure similar to that of the semiconductor device25 shown in FIG. 8(a); however, they are different in structure of theheat spreader. The heat spreader 30 provided to the semiconductor device29 is made of metal, and includes a number of coaxially aligned, tubularportions 30 p of a rectangular shape (almost square in this embodiment)when viewed in a plane. The tubular portions 30 p are exposed throughthe mold resin 5.

[0089] The semiconductor device 33 of the fifth embodiment shown in FIG.8(c) is of a structure similar to that of the semiconductor device 21shown in FIG. 7(a) and FIG. 7(b); however, they are different instructure of the heat spreader. The heat spreader 34 provided to thesemiconductor device 33 is made of metal, and includes a pair ofcomb-shaped portions 34 p provided so as to be fit together with aslight clearance in between. The come-shaped portions 34 p are exposedthrough the mold resin 5.

[0090] Any of the heat spreaders 26, 30, and 34 has a larger exposedarea than the heat-spreading portion 6 (see FIG. 1), which enhances theheat-spreading capability of the semiconductor devices 25, 29, and 33 incomparison with the heat-spreading capability of the semiconductordevice 1.

[0091]FIG. 9(a) is a schematic perspective view showing the structure ofa semiconductor device according to a sixth embodiment of the invention.FIG. 9(b) is s schematic cross section taken along the section lineIX-IX of FIG. 9(a).

[0092] The semiconductor device 37 includes a main body 44 that enclosesa semiconductor chip 45 shaped like a rectangular prism and providedwith an LSI (Large Scale Integrated circuit) and is molded into a flat,almost rectangular prism by a mold resin 38, and a heat spreader 39 (notshown in FIG. 9(b)) attached to cover the main body 44.

[0093] A heat-transmitting member 42 is joined to one surface of thesemiconductor chip 45 through soldering 46. The heat-transmitting member42 is exposed through the mold resin 38 at the center of the surface43T, which is one of a pair of surfaces orthogonal to the thicknessdirection of the main body 44 (hereinafter, referred to as the topsurface). The top surface 43T of the main body 44 is almost flush withthe exposed surface of the heat-transmitting member 42.

[0094] Of the four side surfaces 40 (surfaces parallel to the thicknessdirection of the main body 44) of the mold resin 38, plural lead frames41 (four of them in this embodiment) protrude from a pair of sidesurfaces 40A parallel to each other. The respective lead frames 41extend and penetrate through the mold resin 38 in a directionperpendicular to the side surfaces 40A. The lead frames 41 and theheat-transmitting member 42 can be made of, for example, the samematerial.

[0095] The lead frames 41 are provided to the semiconductor chip 45 onthe opposite side to the heat-transmitting member 42. In other words,the semiconductor chip 45 is sandwiched between the lead frames 41 andthe heat-transmitting member 42. The semiconductor chip 45 is providedwith functional elements and leading electrodes thereof on the surfaceopposing the lead frames 41. On the contrary, none of the functionalelements and leading electrodes thereof is formed on the other surfaceof the semiconductor chip 45.

[0096] Bumps 47 are joined to the leading electrodes formed on thesemiconductor chip 45, and the surface of the semiconductor chip 45 onwhich the bumps 47 are formed is connected wirelessly to the lead frames41 through soldering 46. In short, the semiconductor chip 45 and thelead frames 41 are not only electrically connected, but alsomechanically joined to each other through soldering 46.

[0097] The lead frames 41 are all provided on the surface 43B sideopposite to the top surface 43T (hereinafter, referred to as the bottomsurface) in reference to the thickness direction of the main body 44.The surfaces of the lead frames 41 on the bottom surface 43B side arealmost flush with the bottom surface 43B. The lead frames 41 are exposedto the bottom surface 43B. The both ends 41 a of the lead frames 41protrude from the edge of the mold resin 38 when viewed in a directionperpendicular to the bottom surface 43B.

[0098] The heat spreader 39 extends in substantially parallel with thebottom surface 43B, and extends to cross with the lead frames 41 in adirection almost orthogonal to the lead frames 41 when viewed in adirection perpendicular to the bottom surface 43B. When viewed in adirection perpendicular to the bottom surface 43B, the heat spreader 39has a width slightly narrower than the width of the main body 44, andthe both ends of the heat spreader 39 protrude from the edge of the moldresin 38.

[0099] The both ends 39 a of the heat spreader 39 are shaped like aplate, and is placed on almost the same plane as the lead frames 41. Onthe other hand, the intermediate portion 39 c of the heat spreader 39 inits length direction is provided along the top surface 43T of the mainbody 44. The portions between the both ends 39 a and the intermediateportion 39 c form rising portions 39 b provided along a pair of sidesurfaces 40B, which is another pair of the side surfaces 40 of the mainbody 44, different from the pair of the side surfaces 40A.

[0100] The heat spreader 39 comes in contact with the exposed surface ofthe heat-transmitting member 42 through the mold resin 38. Hence, heatgenerated in the semiconductor chip 45 is transmitted to the heatspreader 39 via the heat-transmitting member 42. On the other hand, theheat spreader 39 is not electrically connected to the semiconductor chip45. In other words, the heat spreader 39 does not contribute toelectrical connection of the semiconductor chip 45.

[0101] A number of plate-shaped portions (fins) 39 p, which are parallelto both the thickness direction of the main body 44 and the lengthdirection of the lead frames 41 and parallel to one another, protrudefrom the intermediate portion 39 c of the heat spreader 39. Thisincreases the surface area of the heat spreader 39.

[0102] The wiring board, on which the semiconductor device 37 ismounted, is provided with electrode pads to which wirings are connected,at the positions respectively corresponding to the protrusions of thelead frames 41 from the mold resin 38, and with the joining pads at thepositions corresponding to the both ends 39 a of the heat spreader 39.

[0103] In this case, by having the bottom surface 43B oppose to thewiring board and joining the protrusions of the lead frames 41 from themold resin 38 to the electrode pads, not only can the semiconductor chip45 be electrically connected to the electrode pads formed on the wiringboard, but also the semiconductor device 37 can be mechanically joinedto the wiring board. In addition, by joining the both ends 39 a to thejoining pads through soldering or the like, the semiconductor device 37can be mechanically joined to the wiring board. Under these conditions,the surface of the semiconductor chip 45, on which the functionalelements are formed, is oriented (faced down) to the wiring board side.

[0104] Because the both ends of the lead frames 41 and the both ends 39a of the heat spreader 39 protrude from the edge of the mold resin 38when viewed in a direction perpendicular to the bottom surface 43B,direct visual inspection of the joints described above becomes possible.The joint state of the semiconductor device 37 to the wiring board canbe thus readily confirmed.

[0105] The joining pads can be electrically isolated from the wirings onthe wiring board. In this case, the heat spreader 39 is joined to thewiring board while being electrically isolated therefrom.

[0106] Heat generated in the semiconductor chip 45 is transmitted to thelead frames 41 and the heat-transmitting member 42 (heat spreader 39)provided respectively in two directions (opposite to each other) withrespect to the semiconductor chip 45, and the heat transmitted to eachcomponent is dissipated into air in two directions along the lengthdirection of the lead frames 41 and in two directions along the lengthdirection of the heat spreader 39, that is, in four directions withrespect to the semiconductor chip 45. Because the heat spreader 39 has alarge area, heat can be spreaded efficiently via the heat spreader 39.

[0107] The main body 44 and the heat spreader 39 may be formednon-detachably. In this case, the semiconductor device 37 as a whole canbe mounted on the wiring board. Alternatively, the main body 44 and theheat spreader 39 may be formed detachably. In this case, the main body44 may be brought into contact with the heat spreader 39 by mounting themain body 44 on the wiring board first, and thence mounting the heatspreader 39 on the wiring board.

[0108] While the embodiments of the invention have been described, itshould be appreciated that the invention can be implemented in otherembodiments. For example, in the semiconductor device 1 according to thefirst embodiment above, the third lead frame 10 may extend toward onlyone side of the semiconductor device 1 when viewed in a directionperpendicular to the bottom surface 43B.

[0109] The semiconductor chip 7 is not necessarily connected wirelesslyto all the first through third lead frames 8, 9, and 10. For example,the third lead frame 10 may be replaced with a lead frame comprisingonly a portion equivalent to the both ends 10 a, that is, a lead framehaving neither the rising portions 10 b nor the intermediate portion 10c, so that the replaced lead frame and the gate electrode 11G areconnected to each other through a bonding wire.

[0110] While the above description described embodiments of theinvention in detail, it should be appreciated that these embodimentsrepresent examples to provide clear understanding of the technicalcontents of the invention, and the invention is not limited to theseexamples. The sprit and the scope of the invention, therefore, arelimited solely by the scope of the appended claims.

[0111] This application corresponds to Japanese Patent Application No.2003-142393 filed with the Japanese Patent Office on May 20, 2003, theentire contents of which are incorporated herein by reference.

What is claimed is:
 1. A semiconductor device having a bottom surfaceand mountable on a wiring board with the bottom surface being opposed tothe wiring board, the semiconductor device comprising: a semiconductorchip; a mold resin encapsulating the semiconductor chip; a first heatspreader joined to the semiconductor chip on the bottom surface sidewith respect to the semiconductor chip, and extending in substantiallyparallel with the bottom surface with both ends thereof protruding froman edge of the mold resin when viewed in a direction perpendicular tothe bottom surface, the first heat spreader being capable of beingjoined to the wiring board by means of the both ends thereof; and asecond heat spreader joined to the semiconductor chip on a top surfaceside opposite to the bottom surface with respect to the semiconductorchip, and extending in substantially parallel with the bottom surface tocross with the first heat spreader with both ends thereof protrudingfrom the edge of the mold resin when viewed in a direction perpendicularto the bottom surface, the second heat spreader being capable of beingjoined to the wiring board by means of the both ends thereof, whereinone of the first and second heat spreaders is a lead frame electricallyconnected to the semiconductor chip.
 2. A semiconductor device accordingto claim 1, wherein: the semiconductor chip falls within an intersectionof the first and second heat spreaders completely when viewed in adirection perpendicular to the bottom surface.
 3. A semiconductor deviceaccording to claim 1, wherein: the first heat spreader is exposed to thebottom surface of the semiconductor device.
 4. A semiconductor deviceaccording to claim 1, wherein: both of the first and second heatspreaders are lead frames electrically connected to the semiconductorchip.
 5. A semiconductor device according to claim 4, wherein: thesemiconductor chip is provided with a field effect transistor having asource electrode and a drain electrode, and the drain electrode iselectrically connected to the first heat spreader, and the sourceelectrode is electrically connected to the second heat spreader.
 6. Asemiconductor device according to claim 1, wherein: the semiconductorchip is connected wirelessly to one of the first and second heatspreaders.
 7. A semiconductor device according to claim 1, wherein: bothof the first and second heat spreaders are lead frames electricallyconnected to the semiconductor chip, and the semiconductor chip isconnected wirelessly to both of the first and second heat spreaders. 8.A semiconductor device according to claim 1, wherein: the second heatspreader has a heat-spreading portion exposed through the mold resin onthe top surface side of the semiconductor device.
 9. A semiconductordevice according to claim 1, further comprising: a third heat spreaderjoined to the second heat spreader and exposed through the mold resin.10. A semiconductor device according to claim 9, wherein: the third heatspreader is provided with a plurality of plate-shaped portions exposedthrough the mold resin.